Proposals have already been made to use the heat of exhaust gases during cold-starting and running of an internal combustion engine in order to raise the temperature of the cooling liquid and/or of the engine lubricating oil very rapidly, thereby considerably reducing fuel consumption.
However, known heat exchangers are relatively heavy and are only useful during a relatively small proportion of the total running time of the engine.
Preferred embodiments of the present invention provide a heat exchanger of the above-specified type, but which is relatively light.